Radio-Frequency Identification (RFID) technology has become widely used in virtually every industry, including transportation, manufacturing, waste management, postal tracking, airline baggage reconciliation, and highway toll management. A typical RFID system includes a plurality of RFID tags, at least one RFID reader or detection system having an antenna for communication with the RFID tags, and a computing device to control the RFID reader. The RFID reader includes a transmitter that may provide energy or information to the tags, and a receiver to receive identity and other information from the tags. The computing device processes the information obtained by the RFID reader.
In general, the information received from an RFID tag is specific to the particular application, but often provides an identification for an article to which the tag is fixed. Exemplary articles include manufactured items, books, files, animals or individuals, or virtually any other tangible articles. Additional information may also be provided for the article. The tag may be used during a manufacturing process, for example, to indicate a paint color of an automobile chassis during manufacturing or other useful information.
The transmitter of the RFID reader outputs RF signals through the antenna to create an electromagnetic field that enables the tags to return an RF signal carrying the information. In some configurations, the transmitter initiates communication, and makes use of an amplifier to drive the antenna with a modulated output signal to communicate with the RFID tag. In other configurations, the RFID tag receives a continuous wave signal from the RFID reader and initiates communication by responding immediately with its information.
A conventional tag may be an “active” tag that includes an internal power source, or a “passive” tag that is energized by the field created by the RFID reader. In either case, the tags communicate using a pre-defined protocol, allowing the RFID reader to receive information from one or more tags. The computing device serves as an information management system by receiving the information from the RFID reader and performing some action, such as updating a database. In addition, the computing device may serve as a mechanism for programming data into the tags via the transmitter.
Conventional antennas for RFID readers have a single inductive loop and operate in a relatively high frequency range, e.g., 3 megahertz (MHz) to 30 MHz. Consequently, these antennas tend to create magnetic fields that suffer from “holes,” i.e., regions in which an RFID tag cannot be read even though the RFID tag is located relatively near the antenna. For example, depending on the orientation and location of the article to which the RFID tag is affixed, in some situations the RFID tag may be centered above a single turn of the inductive loop of the antenna during interrogation. In this situation, substantially equal current may be imposed on opposite sides of the RFID tag, which leads to a cancellation effect. As a result, the RFID tag may not be able to achieve RFID communication with the reader.
In addition, conventional antennas used with desktop RFID readers tend to create magnetic fields that extend horizontally beyond the edges of the antennas. Consequently, articles placed proximate the antenna, e.g., next to the antenna on the desktop, may be inadvertently read by the reader, which can lead to undesired results. For example, books associated with one library patron and located next to an antenna in a library management system may be inadvertently checked out to another patron.